The disclosed invention is in the field of liquid chromatography. Liquid chromatography is used by the art to analyze polymers with regard to molecular size by Size Exclusion Chromatography (SEC) and with regard to chemical composition by High Performance Liquid Chromatography (HPLC). This disclosure relates to HPLC analysis of polymers with regard to chemical composition.
Polyolefin polymers (such as polymers and copolymers comprising polymerized ethylene monomer and/or propylene monomer) have long been analyzed with regard to chemical composition distribution by temperature rising elution fractionation (TREF) and crystallization analysis fractionation (CRYSTAF). However, neither TREF nor CRYSTAF can be used to analyze amorphous polyolefin polymers. Furthermore, both TREF and CRYSTAF require a relatively long analysis time. Therefore, the art turned to HPLC in an attempt to reduce analysis time and to expand the scope of analysis to amorphous polymers. Macko et al. apparently were the first to do so in 2003 by studying the retention of polyethylene standards on silica and zeolite stationary phases (J. Chrom. A, 1002 (2003) 55). Wang, et al. studied the retention of polyethylene and polypropylene by zeolites in 2005 (Macromolecules, V. 38, No. 25 (2005) 10341). Heinz and Pasch used a silica stationary phase to analyze polyethylene—polypropylene blends by HPLC (Polymer 46 (2005) 12040). Albrecht, et al., used a silica stationary phase to analyze ethylene—vinyl acetate copolymers by HPLC (Macromolecules 2007, 40, 5545). Albrecht, et al., used a silica stationary phase to analyze ethylene—propylene copolymers by HPLC (Macromol. Symp. 2007, 257, 46). A remaining problem for the HPLC analysis of polyolefin polymers is the limited separation efficiency obtained by the prior art methods.